Chapter #9: Muscles & Muscle Tissue Flashcards
(101 cards)
1
Q
Muscle Functions
A
- Movement
- Body posture & body position
- Joint stability
- Maintaining body temperature
- Excitability
- Contractility
- Extensibility
- Elasticity
2
Q
Movement
A
voluntary and involuntary
3
Q
Body posture & body position
A
Muscles work to hold us up against gravity
4
Q
Joint Stability
A
Muscles & tendons reinforce joints
5
Q
Maintaining body temperature
A
Muscle contraction produces heat
6
Q
Excitability
A
Membrane potential changes in response to stimulus
7
Q
Contractility
A
Muscle cells shorten
8
Q
Extensibility
A
Muscles cells can lengthen/stretch
9
Q
Elasticity
A
Healthy muscle cells return to their original shape
10
Q
Types of muscle tissue
A
- Skeletal muscle tissue
- Smooth muscle tissue
- Cardiac muscle tissue
11
Q
Skeletal muscle tissue
A
-Voluntary muscle tissue
-Function: movement of body parts
-Striated & multinucleate
-Attaches to & uses skeleton
-Creates the most force
-But: needs the most rest
-Adaptable
12
Q
Smooth muscle tissue
A
-Involuntary muscle tissue
-Function: moves fluids & substances through body
-No striations
-Uninucleate
13
Q
Cardiac muscle tissue
A
-Involuntary muscle tissue
-Function: moves blood through body
*Rate of contraction set by pacemaker cells
-Striated
-Uninucleate
14
Q
Gross Anatomy of Skeletal muscle tissue
A
-innervation
-vascularization
-connective tissue sheaths
15
Q
Innervation
A
-Each muscle receives 1 motor nerve
-Function: nerve ending controls activity
-Motor neuron stimulates muscle fibers to contract
16
Q
What neurotransmitter is released by motor neurons?
A
acetylcholine (always stimulatory)
17
Q
Vascularization
A
-Each muscle receives 1 artery, 1+ vein
-Functions: Bring in nutrients, remove waste
18
Q
Connective Tissue Sheaths
A
-Function: supports muscle, holds muscle together
-Layers:
-Endomysium: innermost layer
-Surrounds individual muscle fibers
-Perimysium: middle layer
-Discrete bundles of muscle fibers grouped together: form fascicles
-Epimysium: outermost layer
-Surrounds entire muscle
19
Q
Skeletal muscle attachments
A
-For skeletal muscle to produce movement, it must attach to bone (or another tough structure)
-Why? Our muscles use our bones like levers
-When a muscle contracts, it pulls (or pushes) on a bone to produce movement
20
Q
Direct vs. Indirect attachment of skeletal muscle attachments
A
-Direct: epimysium of muscle fuses directly to bone (or cartilage)
-Indirect: involves tendons
-Tendon: a band of dense fibrous connective tissue that connects a muscle to a bone
21
Q
Is indirect or direct attachment of skeletal muscle attachment more common?
A
indirect because tendons are stronger and thicker
22
Q
2 points of attachment for a muscle
A
1) Origin: where the muscle attaches to a less movable bone
-Always proximal
-Ex: biceps brachii: long head = lip of glenoid fossa, short head = coracoid process
2) Insertion: where the muscle attaches to a movable bone
-Always distal
-Ex: biceps brachii: radial tubersity
23
Q
Microanatomy of skeletal muscles
A
Skeletal muscle cells (myocytes, muscle fibers) are among largest and longest cells in the body
24
Q
Important terminology for skeletal muscle microanatomy
A
1) Sarcolemma
2) Sarcopla
3) Myofilaments
4) Myofibrils
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Sarcolemma
plasma membrane of muscle fibers
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Sarcoplasm
-cytoplasm of muscle fibers
-Contain high numbers of
A) Glycosomes: organelles that store glycogen
-Importance: glycogen is a polysaccharide that is converted to glucose for ATP production in skeletal muscle
B) Myoglobin: red pigment organelle that stores oxygen
-Importance: oxygen is needed for ATP production
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Myofilaments
-protein filaments in muscle tissue
-Types of contractile myofilaments:
A) Thick filament (myosin)
B) Thin filament (actin)
-Function: actin and myosin interact during muscle contraction
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Myosin FIlaments
-Composed of 6 chains
-4 light chains
-2 heavy chains
-Myosin head found at end of each heavy chain
-Each myosin head has 2 binding sites: 1 for ATP, 1 for actin
-Importance: myosin head uses ATP to link two types of myofilaments during contraction
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Actin filaments
-Chains of G actin proteins with myosin binding sites
-Function: myosin head binds to the myosin binding site of actin during muscle contraction
-Regulatory proteins of actin control if/when myosin head can bind
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2 regulatory proteins associated with actin filaments
1) Tropomyosin: arranged along length of thin filament
Function: blocks myosin binding sites on actin filament when muscle is relaxed
2) Troponin: globular protein associated with tropomyosin
Function: binds tropomyosin to position it on the actin filament
31
Myofibrils
-rod-like organelles of muscle cells
-Myofibrils are made up of bands of myofilaments
-Myofilaments overlap in some regions of the myofibril to produce dark bands
-This is what creates striations of skeletal muscle!
-Each muscle fiber has several myofibrils
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Myofibrils composed of alternating A bands and I bands
1) A band: region of myofibril where actin and myosin filaments overlap
-H zone at the center of A band has only myosin filaments
2) I band: region of myofibril with only actin filaments
-Z disc at center holds the actin filaments in place
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What does an A band and I band create?
Sarcomere
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Sarcomeres
-A sarcomere is the region of a myofibril found between 2 successive Z discs
-Importance: the sarcomere is the smallest contractile unit of skeletal muscle tissue
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What part of the A band and I band make up a single sarcomere?
1 A band and half an I band
36
What happens to a muscle when the sarcomere shortens?
the myofibril becomes shorter, so the muscles cell becomes shorter, so the entire muscle becomes shorter
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Other intracellular structures that regulate muscle contraction
1) T-Tubules
2) Sarcoplasmic reticulum
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T-Tubules
-extensions of the sarcolemma that wrap around deeper myofibrils
-Function: increase surface area of muscle fiber sarcolemma
-Importance: changes in membrane potential can reach myofibrils not in direct contact with sarcolemma
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Sarcoplasmic reticulum
-smooth endoplasmic reticulum of muscle
-Highly branched, wraps around myofibrils
-Form terminal cisterns around T-tubules
-Function: stores and releases intracellular Ca2+ for muscle relaxation & contraction
-Notice: 2 terminal cisterns surround 1 t-tubule to form a triad
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The Neuromuscular Junction
-Definition: site of synapse between a somatic motor neuron and a muscle fiber
-Neurotransmitter released: Acetylcholine (ACh)
-Sarcolemma at synaptic cleft folded to form junctional folds
-Function: folds increase surface area of muscle fiber sarcolemma
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What effect does acetylcholine have on a muscle fiber?
Always stimulatory, always causes contraction
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Why is it advantageous for the sarcolemma at the synaptic cleft to form junction folds?
increases the likelihood that receptor can bind with acetylcholine since surface area is increased
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For stimulation of muscle fiber to occur, to following steps must take place
1) Events at the neuromuscular junction
2) Generation of action potential across sarcolemma
3) Excitation-Contraction Coupling
4) Cross Bridge Formation & Muscle Contraction
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Step 1 for stimulation of muscle fiber: Events at the neuromuscular junction
-transmission of action potential
-Result: ACh is released & binds to chemically-gated ion channels on the sarcolemma
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Step 2 for stimulation of muscle fiber: Generation of action potential across sarcolemma
-ACh binds to and opens ion channels on sarcolemma to create end plate potential (EPP)
-EPP is a graded potential specific to muscle tissue
-EPP depolarizes sarcolemma
-If strong enough: action potential generated on sarcolemma
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Step 3 for stimulation of muscle fiber: Excitation-Contraction Coupling
-Occurs when action potential spreads from sarcolemma to T-tubules
-When action potential arrives at T-tubules: voltage-gated proteins in T-tubules change shape
-When T-tubule proteins change shapeCa2+ channels in terminal cistern forced open
-Result: Ca2+ released from sarcoplasmic reticulum & flows into cytosol of muscle fiber
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Step 4 for stimulation of muscle fiber: Cross Bridge Formation & Muscle Contraction
-Once Ca2+ enters cytosolinteraction between actin and myosin filaments can begin
-Cross bridge: the attachment of myosin to actin
-The Process of Cross Bridge Formation:
A) Ca2+ binds troponintroponin changes shape
B) Change in troponin shape causes tropomyosin to roll to the side
C) When tropomyosin is movedmyosin binding site on actin is exposed
-Myosin head will bind to actin binding site with use of ATP
D) Myosin head splits ATP into ADP + Pi
-This allows myosin head to bind to actin
E) ADP + Pi is released from myosin head, causing the myosin head to bend
-Effect: myosin head “pulls” actin filament
-This is called the power stroke
F) Myosin head binds to another ATP: myosin head detaches from actin binding site
G) The myosin head binds to a different actin binding site
-Steps D-G repeat until muscle contraction ends or ATP/Ca2+ run short
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Ending cross-bridge formation & muscle contraction
-Motor impulses no longer sent to muscle fiber
-Action potential to muscle fiber ends
-Ca2+ is returned to sarcoplasmic reticulum
-When Ca2+ levels in sarcoplasm drop, it can no longer bind to troponin
-Troponin returns to original shape
-Result: Tropomyosin movescovers actin binding sites
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Sliding Filament Model of Contraction
-During contraction, actin filaments “slide” over myosin filaments
-Why? Myosin heads form & break multiple cross-bridges with actin
-Myosin heads “slide” thin filaments toward the center of the A band
-Note: filaments do not change length!
-Effect: when the filaments “slide,” the sarcomere shortens and generates tension in the muscle
-This is why muscle fibers shorten when they contract!
50
Motor Units
-A single motor neuron can serve multiple muscle fibers
-BUT: A single muscle fiber is served by only ONE motor neuron
-Motor unit: a single motor neuron and all the muscle fibers it innervates
51
What is the result of stimulation by 1 motor neuron?
cause a widespread weak contraction; if all stimulated at the same time, it would be a much stronger contraction in one part of the muscle
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Motor Unit rule 1
-when the motor neuron fires: all fibers it innervates will contract
-Fibers innervated by a single motor neuron are spread out over entire muscle: not clumped together!
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Motor Unit rule 2
-number of muscle fibers a single motor neuron innervates influences movement
-Motor neuron innervating few fibers
VS.
-Motor neuron innervating many fibers
54
What is the result on movement for each innervating fiber type?
-few fibers = very precise, fine-tuned control
-many fibers = not as precise
55
Muscle Twitch
-Definition: response of a muscle to a single stimulus
-Measured with a twitch myogram
56
3 phases of a myogram
1) Latent period: first few milliseconds following stimulation
-Excitation-contraction coupling occurs, but no tension observable in muscle
2) Period of contraction
-Active cross-bridge formation with increasing tension
3) Period of relaxation
-Cross bridge formation declines, muscle tension declines to resting value
57
Graded Muscle Contractions
-Definition: sustained muscle contraction that is modified by the nervous system to produce varying amounts of force
-Muscle contractions can be graded 2 ways:
1) Temporal summation: increasing the frequency of stimulation of a muscle
2) Motor Unit summation: increasing the strength of stimulation of a muscle
58
Temporal Summation
-Increasing the firing rate of a motor neuron can generate more force at the muscle
-How does it happen?
-Fire stimuli in rapid successionthe second twitch hits the muscle before the first twitch has ended
-Effect: muscle tension increases
59
Temporal summation can lead to 2 forms of tetanus
1) Unfused (incomplete) tetanus: rate of stimulation creates a sustained & quivering muscle contraction
-ex. when you lift something heavy and your muscles shake
-some relaxation occurs
2) Fused (complete) tetanus: rate of stimulation creates smooth, sustained muscle contraction
-No relaxation occurs
-most force you can possibly produce by the muscle
-can be damaging overtime because the muscle fibers use large amounts of ATP at once
60
Motor unit summation
-Definition: recruitment of additional motor units in a muscle to generate more force during contraction
-How does it happen?
-Increase the number of motor units used over time during contraction
-Size principal of motor unit summation
-Motor units with smallest muscle fibers recruited first
-Motor units with largest muscle fibers recruited last: create most force
-Motor units recruited asynchronously: some contracting, others relaxing
61
Why are motor units recruited asynchronously?
-if you use every muscle fiber at the same time, you will fatigue that muscle really quickly and not be able to use it
-trade-off which ones are resting and working
-allows you to vary the force exerted and duration of exertion
62
Muscle Tone
-Relaxed muscles are always slightly contracted: creates muscle tone
-Does not produce movement
-So why is it important?
-Muscle tone keeps muscle tissue healthy and responsive, stabilizes joints, maintains posture (ex. holding your neck up)
-allows muscles to remain excitable
-Loss of muscle tone leads to loss of responsiveness
-Muscle will not respond to stimuli
-Ex: stroke victims
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Types of Muscle Contraction
-Isotonic contraction
-Isometric Contraction
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Isotonic contraction
-muscle tension develops to overcome the load, muscle shortening occurs
-Two subtypes:
1) Concentric contraction: muscle shortens and does work
-Ex: upward motion of a bicep curl
2) Eccentric contraction: muscle generates force as it lengthens
-Ex: downward motion of a bicep curl
-50% stronger than the concentric contraction
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Isometric Contraction
-tension develops in a muscle, but the length of the muscle does not change
-Occurs when the load is not moved
-Cross-bridge formation still occurs, but: the actin filaments do not slide
-Ex: most muscles responsible for body posture, plank position, wall sits, etc.
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Energy Needs for Contraction
-ATP is the only energy source used directly for contractile activity
-Skeletal muscle stores energy in the form of glycogen
-ATP regenerated as fast as it is used
-3 Pathways used to regenerate ATP:
1) Direct phosphorylation
2) Anaerobic pathways
3) Aerobic pathways
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Direct Phosphorylation
-Creates ATP from ADP + Pi using creatine phosphate (CP)
-Catalyzed by creatine kinase
-1 ATP produced per CP molecule
-Does not require oxygen
-Supplies ~15 s worth of ATP
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Anaerobic Pathways: Glycolysis & Lactic Acid Formation
-Glucose broken down to form 2 ATP & pyruvic acid
-In absence of O2pyruvic acid converted to lactic acid
-Lactic acid not used by musclediffuses into blood
-Does not require oxygen
-Fast method to create ATP
-Drawbacks:
-A lot of glucose used for low ATP yield (2 ATP)
-Lactic acid build-up results in DOMS (delayed onset muscle soreness)
-Stored glycogen, creatine phosphate, & glycolysis provide ~1 minute of ATP
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Aerobic Pathway: Cellular Respiration
-Creates 95% of ATP used by muscle during rest and light to moderate long-term exercise
-Requires pyruvic acid produced in anaerobic pathway
-Requires oxygen and mitochondria
-Produces ~30 ATP, H20, and CO2
-Drawbacks:
-Slow process
-Requires constant O2 and glucose
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Muscle Fatigue
-We can produce ATP: but it is not unlimited
-Muscle fatigue occurs: muscle is physiologically incapable of contracting
-Rate & duration of fatigue depends on activity
-High intensity exercise (ex. HIT workouts) VS.
-Low intensity exercise (ex. marathon running)
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Why is muscle fatigue necessary and important? What happens to muscle fibers if ATP is completely depleted?
-muscle fatigue prevents a muscle cell from running out of ATP because if it runs out of ATP, it dies
-your skeletal muscle cells have other activities to keep them alive that require ATP
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How quickly will high-intensity vs low-intensity exercise cause fatigue? What is the duration of fatigue for each?
-High-intensity exercise = muscle tires out quickly, rate of fatigue is fast, but the duration of fatigue is short
-Low-intensity exercise = muscle tires out at a slower rate, rate of fatigue is slow, but the duration of fatigue is long
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Muscle Contraction: Force
-Force of contraction is determined by the number of cross-bridges formed between myosin and actin filaments
-More cross bridges = more force
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Force of muscle contraction is influenced by 4 factors
1) Frequency of stimulation: temporal summation
2) Number of muscle fibers recruited: motor unit summation
3) Size of muscle fiber
-Bulkier muscle generates more tension, creates more force
-Hypertrophy: increase size of muscle fibers in muscle to increase force generated
-Rate of hypertrophy dependent on genetics, sex, nutrition, etc.
4) Degree of muscle stretch
-Force a muscle creates varies with how much the muscle is stretched
-Length-tension relationship: the maximal force produced will differ based on the degree of muscle stretch or contraction (optimal overlap is going to generate the most force)
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Why can bulkier muscles generate more tension and force?
larger muscle fibers have more myofibrils, more myofibrils have more myofilaments, and more myofilaments mean more cross-bridges that can be formed
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Why can muscle generate less tension when the sarcomeres are stretched? Shortened?
-when the sarcomeres are shortened, there is so much overlap between myofilaments that they cannot move anywhere and cannot form cross-bridges
-when the sarcomeres are stretched, there is no overlap between myofilaments, the myosin heads have nothing to physically attach themselves to and cannot form cross-bridges
-cannot generate a lot of force in either of these situations
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Muscle Contraction: Velocity & Duration
-Fiber type influences velocity & duration of muscle contraction
1) Speed of contraction
-Dependent on:
A) How fast ATP is split: how fast cross bridges can form & break
B) Electrical activity of motor neurons: fast neurons = fast contraction
2) Load and recruitment
Small loads allow faster contraction
More motor unit recruitment = faster contraction
3) Pathway of ATP production
Oxidative fibers: use aerobic pathways
Glycolytic fibers: use anaerobic pathways
-Three fiber types created from different combinations of the above: fast glycolytic, fast oxidative, & slow oxidative
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Slow Oxidation Fibers
-speed of contraction & ATP breakdown = slow
-myoglobin content = high
-glycogen content = low
-fatigue = slow
-mitochondria = many
-capillary supply = many
-example activities = anything endurance
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Fast Oxidative Fibers
-speed of contraction & ATP breakdown = fast
-myoglobin content = high
-glycogen content = intermediate
-fatigue = intermediate
-mitochondria = many
-capillary supply = many
-example activities = sprinting, walking
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Fast Glycolytic Fibers
-speed of contraction & ATP breakdown = fast
-myoglobin content = low (doesn't use oxygen)
-glycogen content = high
-fatigue = fast
-mitochondria = few
-capillary supply = few
-example activities = intense, powerful movement
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Gross Anatomy of Smooth Muscle Tissue
-Hollow organs in the body have smooth muscle tissue
-Most organs have 2 layers of smooth muscle tissue that never contract simultaneously in the same area:
1) Longitudinal layer: muscle fibers run the
length of the organ
-More superficial
2) Circular layer: muscle fibers run the circumference of the organ
-Deep to longitudinal layer
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What organ does not have smooth muscle tissue?
heart has cardiac muscle tissue
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What happens to the organ when the longitudinal layer contracts?
leads to the organ becoming shorter and wider
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What happens to the organ when the circular layer contracts?
organ becomes long and thin
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Differences between smooth muscle fibers and skeletal muscle fibers
1) Smooth muscle fibers are short, spindle-shaped
2) Covered only by endomysium
3) No neuromuscular junctions
4) Smooth muscle fibers have no T-tubules & less sarcoplasmic reticulum
5) Muscle fibers have gap junctions
6) No striations or sarcomeres
7) No troponin
8) Thick and thin filaments arranged diagonally
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No neuromuscular junctions (smooth muscle tissue)
-innervation forms varicosities
-Autonomic fibers have bulb-like swellings scattered over smooth muscle tissue surface
-Importance: creates diffuse junctions
-Wide synaptic clefts that release neurotransmitter to multiple muscle fibers
87
Smooth muscle fibers have no T-tubules & less sarcoplasmic reticulum (smooth muscle tissue)
-Sarcoplasmic reticulum releases only a small amount of Ca2+
-Caveolae: invaginations of of sarcolemma of muscle fiber
-Have Ca2+ ion channels
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Where does the calcium come from in caveolae?
extracellular fluid (outside of the cell)
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Muscle fibers have gap junctions (smooth muscle tissue)
Depolarization spreads from cell to cell
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No striations or sarcomeres (smooth muscle tissue)
-There are still thick and thin filaments, but:
-Fewer thick filaments overall
-Myosin heads found along entire length of thick filament
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No troponin (smooth muscle tissue)
Calmodulin: protein that acts as Ca2+ binding site
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Thick and thin filaments arranged diagonally (smooth muscle tissue)
-Filaments spiral down axis of muscle fiber
-Effect: when a muscle fiber contracts: it twists
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Types of Smooth Muscle
-Unitary smooth muscle
-Multi-unit smooth muscle
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Unitary smooth muscle
-Everything described so far are characteristics of unitary smooth muscle
-Much more commonfound in hollow organs
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Multi-Unit smooth muscle
-Have no gap junctions or spontaneous depolarization
-Muscle fibers are structurally independent
-Forms motor units
-Have graded contractions with recruitment
-Found in arrector pili, smooth muscle of airways, internal eye muscles
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Regulation of Contraction
-Neural Regulation
-Hormones & Local Chemical Factors
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Neural Regulation
-Neurotransmitter can excite or inhibit smooth muscle tissue
-Response is dependent on receptor molecules on sarcolemma
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Hormones & Local Chemical Factors
-Some smooth muscle has no innervation: respond only to local chemicals
-Others spontaneously depolarize
-Act by enhancing or inhibiting Ca2+ entry into sarcoplasm
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Unique Features of Smooth Muscle
1) Response to stretch
2) Length and tension changes
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Response to stretch (smooth muscle tissue)
-Smooth muscle responds to stretch by contracting
-Importance: increases ability to push substances through organ
-Stress-relaxation response: if an organ is filled slowly, it will not contract strongly
101
Length and tension changes (smooth muscle tissue)
-Smooth muscle can stretch more & can generate more tension while stretched
-Can still contract when stretched 150% its length
